Greenhouse gases reached record highs in 2011, says U.N. study

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United Nations agency report says 2011 saw new high for levels of greenhouse gases in Earth's atmosphere

Levels of carbon dioxide now stand at 390.9 parts per million, up 2 ppm on previous year

375 billion tons of carbon dioxide released into atmosphere since 1750, say WMO

Natural carbon sinks are already showing signs of stress and cannot be relied on in future

Concentrations of greenhouse gases in the Earth's atmosphere reached record highs in 2011, according to new data published by the World Meteorological Organization (WMO).

The WMO's annual Greenhouse Gas Bulletin, released Tuesday, reports that carbon dioxide rose to 390.9 parts per million (ppm), up two ppm on 2010 levels.

Carbon dioxide is the single most important greenhouse gas emitted by humans, says the WMO, and the increases recorded last year are in line with average rises seen each year over the last decade.

Combined with average yearly rises of 1.5 ppm during the 1990s, the WMO says radiative forcing (the warming effect on our climate) by long-lived greenhouse gases has now increased 30% since 1990.

"These billions of tons of additional carbon dioxide in our atmosphere will remain there for centuries, causing our planet to warm further and impacting on all aspects of life on Earth," WMO secretary general Michel Jarraud said in a statement.

According to the WMO, about 375 billion tons of carbon has been released into the atmosphere since the industrial revolution began in 1750, with around half this amount being absorbed by carbon sinks. But natural carbon storage facilities like oceans and forests "will not necessarily continue in the future," say the WMO.

"We've already seen that the oceans are becoming more acidic as a result of the carbon dioxide uptake, with potential repercussions for the underwater food chain and coral reefs," Jarraud said in a statement.

The Swiss-based United Nations agency, which uses data from more than 50 countries to compile the report, also detailed rises in other greenhouse gases including methane and nitrous oxide.

Around 60% of methane released into the atmosphere comes from human activities such as farming, rice agriculture, fossil fuel exploitation, landfill and biomass burning, according to the WMO. In 2011, concentrations reached a new high of 1813 parts per billion (ppb), 259% higher than pre-industrial levels.